Effecting change to transmit duty cycle of WLAN transceiver

ABSTRACT

An apparatus has a wireless local area network (WLAN) transceiver and one or more sensors. The sensors are monitored. From time to time, a mitigation level applicable to the apparatus is determined as a function of output from the one or more sensors. The mitigation level is one of multiple mitigation levels, each mitigation level corresponding to a set of configuration changes for a Media Access Control (MAC) layer of the WLAN transceiver. Responsive to determining that the applicable mitigation level has increased from a most recent previously determined mitigation level, the MAC layer is configured to effect a decrease in a transmit duty cycle of the WLAN transceiver. Responsive to determining that the applicable mitigation level has decreased from a most recent previously determined mitigation level, the MAC layer is configured to effect an increase in the transmit duty cycle of the WLAN transceiver.

TECHNICAL FIELD

This disclosure is related generally to an apparatus having a wirelesslocal area network (WLAN) transceiver, and more specifically totechniques for mitigating emissions from the RF components of the WLANtransceiver and any co-located additional wireless transceivers.

BACKGROUND

Specific Absorption Rate (SAR) is a measure of the rate of radiofrequency (RF) energy absorption by the body from a wirelesscommunication device. SAR provides a straightforward means for measuringthe RF exposure characteristics of wireless communication devices toensure that they are within safety guidelines set by regulatory bodiessuch as the Federal Communications Commission (FCC).

In order to determine compliance, a wireless communication device istested while operating at its highest transmit power level in all thefrequency bands in which it operates, and in various specific positionsagainst a dummy head and body, to simulate the way different userstypically make use of the device. Currently, rules from most regulatorybodies require reductions in transmit power as the only means to ensurecompliance.

However, reducing transmit power may result in link instability ordisconnection.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of an example network architecture involvingan apparatus having a wireless local area network (WLAN) transceiver;

FIG. 2-1 and FIG. 2-2 illustrate alternative example methods to beimplemented by a mitigation manager;

FIG. 3-1 and FIG. 3-2 illustrate alternative example methods forhandling an indication of a mitigation level; and

FIG. 4 and FIG. 5 illustrate example functional block diagrams ofexample apparatuses.

DETAILED DESCRIPTION

In an apparatus having a wireless local area network (WLAN) transceiver,there are radio frequency (RF) emissions from the radio.

A proximity sensor internal to the apparatus may indicate proximity ofthe apparatus to a particular body part of a human, for example a heador a lap. Concerns regarding meeting safety guidelines may be higherwhen the proximity sensor indicates proximity to the particular bodypart than when the proximity sensor indicates no proximity.

A thermal sensor internal to the apparatus may be positioned proximateto the WLAN transceiver to sense thermal energy. Assuming no othersources of RF emissions in the apparatus, the level of RF emissions ispositively correlated to the transmit power and the transmit duty cycleof the WLAN transceiver. The temperature output by the thermal sensor isgenerally indicative of the level of RF emissions. Aside from concernsregarding meeting safety guidelines, the output of the thermal sensormay be indicative of the risk of thermal damage to internal componentsof the apparatus.

Although the temperature and proximity cannot be directly controlled,this document proposes setting configuration parameters of a MAC layerof the WLAN transceiver to effect changes to the transmit duty cycle ofthe WLAN transceiver. All else being unchanged, reducing the transmitduty cycle of the WLAN transceiver is expected to reduce the temperaturesensed by the thermal sensors and the RF emissions of the apparatus as awhole, because the WLAN transceiver's power amplifier and othercomponents generating thermal energy are in use for less time.

The apparatus may include one or more additional wireless transceivers,for example a wireless personal area network (WPAN) transceiver or acellular modem. A thermal sensor may be positioned proximate to theadditional wireless transceiver to sense thermal energy. The level of RFemissions is positively correlated to the transmit power and thetransmit duty cycle of the additional wireless transceivers.

In practice, the transmit power and transmit duty cycle of theadditional wireless transceiver are dynamic and not fixed, and thetransmit power of the WLAN transceiver is dynamic and not fixed. Thusreducing the transmit duty cycle of the WLAN transceiver effected bymaking particular MAC-layer configuration changes to the WLANtransceiver may not actually reduce the temperature sensed by thethermal sensors or the RF emissions of the apparatus as a whole.Accordingly, this document proposes monitoring the output of the one ormore sensors and state information for the additional wirelesstransceiver, determining an applicable mitigation level as a function ofthe output of the sensors and the state information, and makingparticular MAC-layer configuration changes to the WLAN transceiver toeffect changes in the transmit duty cycle of the WLAN transceiver, wherethe particular MAC-layer configuration changes correspond to theapplicable mitigation level that has been determined.

If the applicable mitigation level is indicative of temperature and RFemissions at satisfactory levels, the MAC-layer configuration changes tothe WLAN transceiver do not impose any particular constraints on thetransmit duty cycle of the WLAN transceiver. If the mitigation level isindicative of temperature or RF emissions at levels warranting concern,then the MAC-layer configuration changes to the WLAN transceiver mayeffect a significantly reduced transmit duty cycle of the WLANtransceiver. For intermediate mitigation levels, the MAC-layerconfiguration changes to the WLAN transceiver may effect minor changesto the transmit duty cycle of the WLAN transceiver.

FIG. 1 is an illustration of an example network architecture 100involving an apparatus 102 having a wireless local area network (WLAN)transceiver 104 compatible with one or more WLAN technologies.

The WLAN transceiver 104 is operable to connect to a wireless accesspoint (AP) 106 that is compatible with one or more of the one or moreWLAN technologies. For example, such technologies may include, or bebased on, any one or any combination of the IEEE 802.11 family of WLANstandards (as described in IEEE Std. 802.11™-2012 published 29 Mar. 2012by IEEE Computer Society). The term “Wi-Fi®” refers to interoperableimplementations of the IEEE 802.11 family of WLAN standards certified bythe Wi-Fi Alliance.

A WLAN driver 108 is installed in the apparatus 102, to enable controland monitoring of the WLAN transceiver 104, as illustrated by an arrow110. A medium access control (MAC) layer 112 of the WLAN transceiver 104is implemented in software and is configurable through the setting ofvarious MAC-layer parameters. Some of the MAC-layer parameters, such asinterframe spacing parameters and backoff parameters, are timingparameters that affect the transmit duty cycle of the WLAN transceiver104. For example, increases in the duration of these timing parametersincreases the time that the transmitter of the WLAN transceiver 104 isoff, thus reducing the transmit duty cycle of the WLAN transceiver 104.

A mitigation manager 114 in the apparatus 102 determines a “mitigationlevel” that is applicable to the apparatus 102. Further details abouthow the applicable mitigation level is determined are described withrespect to FIG. 3. An indication of the applicable mitigation level, asdetermined by the mitigation manager 114, is provided to the WLAN driver108, as illustrated by an arrow 116. Each mitigation level correspondsto a particular set of MAC-layer configuration changes to the WLANtransceiver. Responsive to being provided the indication of theapplicable mitigation level, the WLAN driver 108 may adjust settings ofconfiguration parameters of the MAC layer 112 to effect a change in thetransmit duty cycle of the WLAN transceiver 104. Further details abouthow the WLAN driver 108 handles the indication of the applicablemitigation level are described with respect to FIG. 4.

The apparatus 102 has one or more sensors, and the mitigation manager114 determines the applicable mitigation level as a function of outputfrom the one or more sensors.

The one or more sensors may include, for example, a thermal sensor 118positioned proximate to components of the WLAN transceiver 104 thatgenerate thermal energy (figuratively illustrated by curves 120). Suchcomponents may include, for example, a power amplifier of the WLANtransceiver 104. Output of the thermal sensor 118 may be read by aprocessor (not shown) and provided, as illustrated by an arrow 122, tothe mitigation manager 114. The output of the thermal sensor 118 may beprocessed (for example, filtered and/or averaged) by the processorbefore being provided to the mitigation manager 114.

The one or more sensors may include, for example, one or more proximitysensors 124 operative to detect that the apparatus 102 is positionedproximate to a human, or proximate to a particular body part of thehuman, for example, to a head or a lap. Output of the proximity sensors124 may be read by a processor (not shown) and provided, as illustratedby an arrow 126, to the mitigation manager. The output of the proximitysensors 124 may be processed by the processor before being provided tothe mitigation manager 114.

The apparatus 102 may optionally have one or more additional wirelesstransceivers capable of producing radio frequency (RF) emissions, forexample, a cellular modem 134 compatible with one or more cellularnetwork technologies or a wireless personal area network (WPAN)transceiver (not shown).

The cellular modem 134 is operable to connect to a wireless base station136 that is compatible with one or more of the one or more cellularnetwork technologies. For example, such technologies may include, or bebased on, Code Division Multiple Access (CDMA), Global System for Mobilecommunications (GSM), General Packet Radio Service (GPRS), Enhanced Datarates for GSM Evolution (EDGE), Universal Mobile TelecommunicationsSystem (UMTS®), High Speed Packet Access (HSPA), Evolved HSPA (HSPA+),Long-Term Evolution (LTE), or LTE-Advanced.

If the apparatus 102 includes the cellular modem 134, the thermal sensor118 may be positioned proximate to components of the cellular modem 134that generate thermal energy (figuratively illustrated by curves 140).Such components may include, for example, a power amplifier of thecellular modem 134. There may be a single thermal sensor positionedproximate to the WLAN transceiver 104 and to the cellular modem 134.Alternatively, there may be a thermal sensor positioned proximate to theWLAN transceiver 104 and another thermal sensor positioned proximate tothe cellular modem 134.

If the apparatus 102 includes the cellular modem 134, a cellular driver138 is installed in the apparatus 102, to enable control and monitoringof the cellular modem 134, as illustrated by an arrow 142. Stateinformation regarding the cellular modem 134, obtained via themonitoring function of the cellular driver 138, is provided to themitigation manager 114, as illustrated by an arrow 144. The stateinformation may include, for example, any one or any combination of thefollowing: an indication of the type of cellular network with which thecellular modem 134 is connected, an indication of the cellular dutycycle of the cellular modem 134, an indication of the cellular transmitpower of the cellular modem 134, and an on/off indication whether thecellular modem 134 is currently transmitting. The mitigation manager 114determines the applicable mitigation level as a function of the stateinformation.

An example method to be implemented by the mitigation manager 114 isillustrated in FIG. 2-1. At 202, the mitigation manager 114 monitors theone or more sensors. At 204, the mitigation manager 114 determines themitigation level that is currently applicable to the apparatus 102. Thisdetermination by the mitigation manager 114 of the applicable mitigationlevel occurs from time to time. For example, the mitigation manager 114may poll from time to time for output of the sensors (and, ifappropriate, for state information of any additional wirelesstransceivers) from time to time, and then determine the applicablemitigation level. In another example, the mitigation manager 114 maywait at 202 to be provided updates of the (possibly processed) output ofthe thermal sensor 118 and/or the (possibly processed) output of theproximity sensors 123 (and/or, if appropriate, the state information ofany additional wireless transceivers), and may determine the applicablemitigation level responsive to receiving the updates.

At 206, responsive to determining the currently applicable mitigationlevel, the mitigation manager 114 compares the currently applicablemitigation level to the most recent previously applicable mitigationlevel. If there is no change in the mitigation level, as checked at 208,then as indicated by an arrow 212 the mitigation manager 114 againmonitors at 202 the one or more sensors. If the mitigation level haschanged, as checked at 208, the mitigation manager 114 causes anindication of the currently applicable mitigation level to be providedto the WLAN driver 108 at 210, and then as indicated by an arrow 214again monitors at 202 the one or more sensors.

In an alternative example method, illustrated in FIG. 2-2, themitigation manager 114 may cause an indication of the currentlyapplicable mitigation level to be provided to the WLAN driver 108 at 210responsive to determining at 204 the currently applicable mitigationlevel, as indicated by an arrow 216, without comparing the currentlyapplicable mitigation level to the previously applicable mitigationlevel.

As noted above, each of the multiple mitigation levels corresponds toparticular set of MAC-layer configuration changes to the WLANtransceiver. In the following discussion, the example of four mitigationlevels {0, 1, 2, 3} is used. In other examples, there may be only two orthree mitigation levels, or there may be more than four mitigationlevels. The greater the number of mitigation levels, the greater thenumber of sets of MAC-layer configuration changes that can be applied tothe WLAN transceiver to effect changes to the transmit duty cycle of theWLAN transceiver. As discussed in more detail herein, the highestmitigation level may correspond to an aggressive course of action tosignificantly reduce the transmit duty cycle of the WLAN transceiver104, and the lowest mitigation level may correspond to not imposing anyadditional constraints on the transmit duty cycle of the WLANtransceiver 104.

As mentioned above, the mitigation manager 114 determines the applicablemitigation level as a function of the output of the one or more sensors.Various examples are illustrated below, simply to illustrate certainconcepts. Other methods for determining (as a function of the output ofthe one or more sensors) which mitigation level applies may be usedinstead.

For example, the mitigation manager 114 may determine the mitigationlevel solely as a function of temperature, as listed in Table 1:

TABLE 1 Mitigation Temperature T Level (ML) threshold conditions ML = 3if (45° C. ≦ T) else ML = 2 if (35° C. ≦ T < 45° C.) else ML = 1 if (30°C. ≦ T < 35° C.) else ML = 0 (T < 30° C.)

In another example, where the apparatus 102 includes the thermal sensor118 and the proximity sensor 124, the mitigation manager 114 maydetermine the mitigation level as a function of temperature andproximity, as listed in Table 2:

TABLE 2 Mitigation Level (ML) Temperature T and proximity conditions ML= 3 if (45° C. ≦ T) AND close proximity to body part else ML = 2 if (35°C. ≦ T < 45° C.) AND close proximity to body part else ML = 1 if (30° C.≦ T < 35° C.) AND close proximity to body part else ML = 0 (T < 30° C.)OR no proximity to body part

For example, if output of the proximity sensor 124 indicates noproximity to a body part of interest (for example, a head or a lap) of ahuman, then the mitigation manager 114 determines an applicablemitigation level of 0. If output of the proximity sensor 124 indicatesproximity to a body part of interest of a human, then the mitigationmanager 114 determines the applicable mitigation level based on theoutput of the thermal sensor 118.

In yet another example, where the apparatus 102 includes the thermalsensor 118 and the cellular modem 134, the mitigation manager 114 maydetermine the mitigation level as a function of temperature and whetherthe cellular modem 134 is currently transmitting, as listed in Table 3:

TABLE 3 Mitigation Level (ML) Temperature T and Cellular TX on/offconditions ML = 3 if (45° C. ≦ T) AND (cellular TX = on) else ML = 2 if(35° C. ≦ T < 45° C.) AND (cellular TX = on) else ML = 1 if (30° C. ≦ T< 35° C.) AND (cellular TX = on) else ML = 0 (T < 30° C.) OR (cellularTX = on)

In a further example, where the apparatus 102 includes the thermalsensor 118 and the cellular modem 134, the mitigation manager 114 maydetermine the mitigation level as a function of the cellular transmitpower, the cellular duty-cycle, and the temperature, as listed for thecase of LTE in Table 4:

TABLE 4 Mitigation Cellular Tx Power P and Cellular Transmit Duty-CycleD Level (ML) and Temperature T conditions ML = 3 if (21 dBm ≦ P) OR (80%≦ D) OR (45° C. ≦ T) else ML = 2 if (19 dBm ≦ P < 21 dBm) OR (70% ≦ D <80%) OR (35° C. ≦ T < 45° C.) else ML = 1 if (15 dBm ≦ P < 19 dBm) OR(50% ≦ D < 70%) OR (30° C. ≦ T < 35° C.) else ML = 0 (P < 15 dBm) AND (D< 50%) AND (T < 30° C.)

For example, if the cellular network type is LTE, the cellular transmitpower P is 16 dBm, the cellular transmit duty-cycle is 48% and thetemperature is 29° C., the mitigation manager 114 determines that theapplicable mitigation level is 1.

In another example, if the cellular network type is LTE, the cellulartransmit power P is 18 dBm, the cellular transmit duty-cycle is 76% andthe temperature is 34° C., the mitigation manager 114 determines thatthe applicable mitigation level is 2.

Different cellular network types have different traffic and powerspectrum profiles, which translate to different contributions to thermalenergy. Accordingly, it is expected that the function used by themitigation manager 114 to determine the mitigation type as a function oftemperature, cellular transmit power, and cellular the set of thresholdconditions relating to transmit power and transmit duty cycle for onecellular network type will differ from the set of threshold conditionsrelating to transmit power and transmit duty cycle for another cellularnetwork type.

FIG. 3-1 illustrates an example method for handling an indication of amitigation level, the method to be implemented by the WLAN driver 108.At 302, the WLAN driver 108 receives the indication of the applicablemitigation level determined by the mitigation manager 114. Responsive toreceiving the indication of the applicable mitigation level, the WLANdriver 108 compares at 304 the received applicable mitigation level tothe most recent previously applicable mitigation level. If there is nochange in the mitigation level, as checked at 306, then the WLAN driver108 waits, as indicated by an arrow 308, until a next indication ofapplicable mitigation level determined by the mitigation manager isreceived at 302. If the mitigation level has changed, as checked at 306,the WLAN driver 108 configures at 310 the MAC layer 112 of the WLANtransceiver 104 with the set of MAC-layer configuration changes thatcorresponds to the applicable mitigation level, to effect a change inthe transmit duty cycle of the WLAN transceiver 104, and then asindicated by an arrow 312 waits until a next indication of applicablemitigation level determined by the mitigation manager is received at302.

In an alternative example method, illustrated in FIG. 3-2, the WLANdriver 108 may configure the MAC layer 112 at 310 responsive toreceiving at 302 the indication of the applicable mitigation level, asindicated by an arrow 314, without comparing the currently applicablemitigation level to the previously applicable mitigation level.

Various techniques to affect the transmit duty cycle of the WLANtransceiver 104 are suggested in this document.

Technique a: Indicate Power-Save Mode on Every Uplink Data Frame

Coarse tuning of the transmit duty cycle of the WLAN transceiver may beeffected through imposition of certain power managementcharacteristics/features. As this is an aggressive course of action thatis expected to significantly reduce the transmit duty cycle of the WLANtransceiver 104, this technique may be an appropriate choice when thehighest mitigation level is applicable to the apparatus 102.

Power management techniques are described in section 10.2 of Std802.11™-2012. When a station (STA) transmits to an AP an uplink dataframe that indicates that the STA is operating in a power-save mode, theAP will respond with a downlink frame, and the STA will not transmitanother uplink data frame to the AP until after the STA receives thatdownlink frame from the AP. This has the effect of reducing the transmitduty cycle of the STA—even if the STA does not actually power down anyof its components—because the STA transmits only one uplink data frameat a time and must wait for a downlink frame from the AP beforetransmitting a next uplink data frame.

Thus having the WLAN driver 108 configure the MAC layer 112 of the WLANtransceiver 104 to indicate in every uplink data frame that the WLANtransceiver 104 is operating in power-save mode may result in asignificant decrease in the transmit duty cycle of the WLAN transceiver104, even if the WLAN transceiver 104 does not actually power down anyof its components. For example, if the uplink data frames sent by theWLAN transceiver 104 and the downlink frames sent by the AP 110 are thesame size and are sent at the same data rate, then implementing thismitigation technique of indicating power-save mode in each uplink dataframe will reduce the transmit duty cycle of the WLAN transceiver 104 to50%. The WLAN driver 108 may configure the MAC layer 112 of the WLANtransceiver 104 to set the Power Management sub-field in the FrameControl field of every uplink data frame to the bit-value 1 (one).

Technique B: Change Interframe Spacing Parameters

Fine tuning of the transmit duty cycle of the WLAN transceiver 104 maybe effected through changes to interframe spacing parameters. How thistechnique is applied will depend on whether Quality of Service (QoS)functionality is currently enabled in the WLAN transceiver 104. The WLANtransceiver 104 will be denoted non-QoS STA if the apparatus 102 is alegacy station incapable of implementing QoS functionality, or if theapparatus 102, despite the WLAN transceiver 104 being capable ofimplementing QoS functionality, is currently connected to an AP that hasnot turned on (that is, activated or enabled) QoS functionality for theWLAN that the WLAN transceiver 104 has joined. The WLAN transceiver 104will be denoted QoS STA if the WLAN transceiver 104 is capable ofimplementing QoS functionality and is currently connected to an AP thathas turned on (that is, activated or enabled) QoS functionality for theWLAN that the WLAN transceiver 104 has joined.

A carrier sense multiple access with collision avoidance (CSMA/CA)access method known as Distributed Coordination Function (DCF),described in section 9.2.2 of Std 802.11™-2012, mandates that atransmitting STA must verify that the wireless medium is idle for aminimum specified duration before attempting to transmit. The minimumspecified duration is denoted DCF InterFrame Space (DIFS). Increasingthe DIFS may reduce the transmit duty cycle of a non-QoS STA, becausethe STA is required to verify that the wireless medium is idle for alonger duration before attempting to transmit. Decreasing the DIFS mayincrease the transmit duty cycle of the STA, because the STA is requiredto verify that the wireless medium is idle for a shorter duration beforeattempting to transmit.

The DIFS is calculated as follows:DIFS=SIFS+DIFSn×SlotTime  [Eqn. 1]

where SIFS is the Short InterFrame Space, the SlotTime is a duration ofa slot, and DIFSn is an integer value whose default value is 2.

Thus having the WLAN driver 108 configure the WLAN transceiver 104 ofthe non-QoS STA with a DIFSn value of 4 may slightly reduce the transmitduty cycle compared to when the WLAN transceiver 104 is configured withthe default DIFSn value of 2. Likewise, having the WLAN driver 108configure the WLAN transceiver 104 of the non-QoS STA with a DIFSn valueof 15 may slightly reduce the transmit duty cycle compared to when theWLAN transceiver 104 is configured with a DIFSn value of 4.

A transmitting QoS STA must verify that the wireless medium is idle foran access-category-dependent minimum specified duration beforeattempting to transmit. The minimum specified duration is denotedArbitration InterFrame Space (AIFS). The AIFS[ac] for the accesscategory ac is calculated as AIFSN[ac] multiplied by the duration of asingle time slot, where AIFSN stands for AIFS number, and is an integervalue between 0 and 15.AIFS[ac]=AIFSN[ac]×SlotTime  [Eqn. 2]

Increasing the AIFSN for a particular access category may reduce thetransmit duty cycle of a QoS STA, because the QoS STA is required toverify that the wireless medium is idle for a longer duration beforeattempting to transmit frames from the queue for that access category.Decreasing the AIFSN for a particular access category may increase thetransmit duty cycle of the STA, because the STA is required to verifythat the wireless medium is idle for a shorter duration beforeattempting to transmit from the queue for that access category.

Thus having the WLAN driver 108 configure the WLAN transceiver 104 ofthe QoS STA with an increment of 3 (for example) to the AIFSN[ac] valuesassigned by the AP may slightly reduce the transmit duty cycle comparedto when the WLAN transceiver 104 is configured with the AIFSN[ac] valuesassigned by the AP. Likewise, having the WLAN driver 108 configure theWLAN transceiver 104 of the QoS STA with maximal AIFSN[ac] values of 15may slightly reduce the transmit duty cycle compared to when the WLANtransceiver 104 is configured with an increment of 3 (for example) tothe AIFSN[ac] values assigned by the AP.

Technique C: Adjusting Back-Off Parameters

An aspect of DCF is that in the event of a collision, the STA chooses arandom back-off number between CWmin and CWmax, and then waits aback-off duration (equal to a slot duration multiplied by the randomback-off number) before again attempting to transmit. If that nextattempt is unsuccessful, the STA then waits twice that duration beforeagain attempting to transmit.

Increasing CWmin may have the effect of reducing the transmit duty cycleof the STA, because the back-off duration that the STA waits (after anunsuccessful attempt to transmit) before attempting again to transmit islonger. Decreasing CWmin may have the effect of increasing the transmitduty cycle of the STA, because the back-off duration that the STA waits(after an unsuccessful attempt to transmit) before attempting again totransmit is shorter.

Thus having the WLAN driver 108 configure the WLAN transceiver 104 withCWmin=64 may slightly reduce the transmit duty cycle compared to whenthe WLAN transceiver 104 is configured with CWmin=31. Likewise, havingthe WLAN driver 108 configure the WLAN transceiver 104 with CWmin=256may slightly reduce the transmit duty cycle compared to when the WLANtransceiver 104 is configured with CWmin=64.

Technique D: Faking Collisions

As noted above, a STA that has experienced a collision while attemptingto transmit will wait a random back-off duration before again attemptingto transmit. Waiting a random back-off duration even when no collisionhas occurred may have the effect of reducing the transmit duty cycle ofthe STA, because the STA waits after successful transmissions beforeattempting a further transmission.

Thus having the WLAN driver 108 configure the WLAN transceiver 104 tofool its MAC layer 112 into reacting as though a collision has occurred,even when the WLAN transceiver 104 has transmitted without collisions,may reduce the transmit duty cycle.

Thus the WLAN driver 108 may configure the MAC layer 112 with the set ofMAC-layer configuration changes that correspond to the applicablemitigation level in accordance with any one or any combination of thesetechniques or other suitable techniques.

Examples of mitigation levels and sets of MAC-layer configurationchanges to effect changes in the transmit duty cycle of the WLANtransceiver 104 are provided in the following tables:

TABLE 5 Mitigation Techniques A Level Techniques A and B (QoS) and B(non-QoS) 3 indicate PS mode (in Frame indicate PS mode Control field)in every UL (in Frame Control field) data frame in every UL data frame 2set AIFSN[ac] = 15 set DIFSn = 15 1 set AIFSN[ac] = AIFSN[ac]_(AP) + 3set DIFSn = 4 0 set AIFSN[ac] = AIFSN[ac]_(AP) set DIFSn = 2

TABLE 6 Mitigation Level Techniques A and C 3 indicate PS mode (in FrameControl field) in every UL data frame 2 set CWmin = 256 1 set CWmin = 640 set CWmin = 31

TABLE 7 Mitigation Techniques A, B Level Techniques A, B (QoS) and C(non-QoS) and C 3 indicate PS mode (in Frame Control indicate PS modefield) in every UL data frame (in Frame Control field) in every UL dataframe 2 set AIFSN[ac] = 15 and set DIFSn = 15 and CWmin = 256 CWmin =256 1 set AIFSN[ac] = AIFSN[ac]_(AP) + 3 set DIFSn = 4 and and CWmin =64 CWmin = 64 0 set AIFSN[ac] = AIFSN[ac]_(AP) and set DIFSn = 2 andCWmin = 31 CWmin = 31

FIG. 4 is an example functional block diagram of an example apparatus402. The apparatus 402 is an example of apparatus 102. The apparatus 402has an internal bus 404 to which the WLAN transceiver 104 and the one ormore sensors (for example, the thermal sensor 118 and/or the proximitysensor 124) are coupled. If the apparatus 402 includes the cellularmodem 134, then the cellular modem 134 is coupled to the internal bus404. The apparatus 402 comprises at least one host processor 406 coupledto the internal bus 404 and a memory 408 coupled to the internal bus404. The memory 408 stores an operating system 410, various applications412, and data 414 for use by the operating system 410 or by the variousapplications 412 or by both. The memory 408 also stores the WLAN driver108 and the mitigation manager 114, and if appropriate, the cellulardriver 138.

The host processor 406 reads the output of the one or more sensors,optionally processes the output, and provides the (possibly processed)output to the mitigation manager 114, which is executed by the hostprocessor 406. If appropriate, the host processor 406 obtains the stateinformation for the cellular modem 134 via the cellular driver 138,which is executed by the host processor 406, and provides the stateinformation to the mitigation manager 114. The applicable mitigationlevel determined by the mitigation manager 114 is provided by the hostprocessor 406 to the WLAN driver 108, which is executed by the hostprocessor 406.

The apparatus 402 may comprise one or more user input/output components420 are coupled to the internal bus 404. A non-exhaustive list ofexamples for the user input/output components 420 includes a displayscreen, a touch screen, an optical pad, a keyboard, a keypad, pressablebuttons, a trackball, a trackpad, a thumbwheel, a microphone, a speaker,and the like. The apparatus 402 may optionally comprise one or moreserial ports 422 (for example, universal serial bus (USB) or micro-USBports) coupled to the internal bus 404. The apparatus 402 may optionallycomprise one or more additional communication subsystems 424, forexample, a wired communication subsystem, a wireless personal areanetwork communication subsystem, a near field communications (NFC)subsystem, a global positioning system (GPS) subsystem, and the like.

The apparatus 402 comprises a power subsystem 430 that supplies power tothe various electronic components in the apparatus 402. The powersubsystem 430 may be any form of power supply, such as a conventionalrechargeable battery (removable or non-removable), a fuel cell system, asolar cell, or the like, or any combination thereof. The apparatus 402in some implementations may be electrically connectable to a fixed powersupply such as a wall outlet. However, in those cases where the powersubsystem 430 supports the portability of the apparatus 402, theapparatus effectively comprises a mobile wireless communication device.

The apparatus 402 may comprise other components that are not illustratedin FIG. 4 so as not to obscure the description of the concepts ofinterest.

FIG. 5 is an example functional block diagram of an example apparatus502. The apparatus 502 is another example of apparatus 102. Theapparatus 502 has an internal bus 504 to which an integrated circuit 552is coupled. The apparatus 502 comprises at least one host processor 506coupled to the internal bus 504 and a memory 508 coupled to the internalbus 504. The memory 508 stores an operating system 510, variousapplications 512, and data 514 for use by the operating system 510 or bythe various applications 512 or by both. The memory 508 also stores theWLAN driver 108 and the cellular driver 138. The proximity sensor 124 iscoupled to the internal bus 504.

The integrated circuit 552 has an internal bus 554, to which the WLANtransceiver 104, the cellular modem 138, and the one or more thermalsensors 120 are coupled. The integrated circuit 552 comprises at leastone processor 556 coupled to the internal bus 554 and a memory 558coupled to the internal bus 554. The memory 558 stores the mitigationmanager 114.

The processor 556 reads the output of the one or more thermal sensors120, optionally process the output, and provides the (possiblyprocessed) output to the mitigation manager 114, which is executed bythe processor 556. The host processor 506 obtains the state informationfor the cellular modem 134 via the cellular driver 138, which isexecuted by the host processor 506, and provides the state informationto the mitigation manager 114. The applicable mitigation leveldetermined by the mitigation manager 114 is provided by the hostprocessor 506 to the WLAN driver 108, which is executed by the hostprocessor 506.

The apparatus 502 comprises one or more user input/output components 520are coupled to the internal bus 504. A non-exhaustive list of examplesfor the user input/output components 520 includes a display screen, atouch screen, an optical pad, a keyboard, a keypad, pressable buttons, atrackball, a trackpad, a thumbwheel, a microphone, a speaker, and thelike. The apparatus 502 may optionally comprise one or more serial ports522 (for example, universal serial bus (USB) or micro-USB ports) coupledto the internal bus 504. The apparatus 502 may optionally comprise oneor more additional communication subsystems 524, for example, a wiredcommunication subsystem, a wireless personal area network communicationsubsystem, a near field communications (NFC) subsystem, a globalpositioning system (GPS) subsystem, and the like.

The apparatus 502 comprises a power subsystem 530 that supplies power tothe various electronic components in the apparatus 502. The powersubsystem 530 may be any form of power supply, such as a conventionalrechargeable battery (removable or non-removable), a fuel cell system, asolar cell, or the like, or any combination thereof. The apparatus 502in some implementations may be electrically connectable to a fixed powersupply such as a wall outlet. However, in those cases where the powersubsystem 530 supports the portability of the apparatus 502, theapparatus effectively comprises a mobile apparatus.

The apparatus 502 may comprise other components that are not illustratedin FIG. 5 so as not to obscure the description of the concepts ofinterest.

Other functional block diagrams are contemplated, with the functionsdescribed above distributed among different components, integratedcircuits, chipsets, memories, and processors.

What is claimed is:
 1. A method in an apparatus having a wireless localarea network (WLAN) transceiver, the method comprising: monitoring oneor more sensors in the apparatus; from time to time, determining fromamong multiple mitigation levels a mitigation level applicable to theapparatus as a function of output from the one or more sensors;responsive to determining that the applicable mitigation level hasincreased from a most recent previously determined mitigation level,configuring a Media Access Control (MAC) layer of the WLAN transceiverto effect a decrease in a transmit duty cycle of the WLAN transceiver,wherein configuring the MAC layer of the WLAN transceiver to effect adecrease in the transmit duty cycle comprises increasing one or moreinterframe spacing parameters of the MAC layer, and configuring the WLANtransceiver to effect an increase in the transmit duty cycle comprisesdecreasing the one or more interframe spacing parameters; and responsiveto determining that the applicable mitigation level has decreased from amost recent previously determined mitigation level, configuring the MAClayer of the WLAN transceiver to effect an increase in the transmit dutycycle of the WLAN transceiver.
 2. The method as claimed in claim 1,wherein the one or more sensors comprise a proximity sensor andmitigation levels are negatively correlated with a distance of theapparatus to a human head or to a human lap as sensed by the proximitysensor.
 3. The method as claimed in claim 1, wherein the one or moresensors comprise a thermal sensor positioned close enough to a poweramplifier of the WLAN transceiver to sense thermal energy generated bythe power amplifier and mitigation levels are positively correlated withtemperatures as sensed by the thermal sensor.
 4. The method as claimedin claim 1, wherein the apparatus comprises an additional wirelesstransceiver and the applicable mitigation level is determined as afunction of state information for the additional wireless transceiver.5. The method as claimed in claim 4, wherein the one or more sensorscomprise a thermal sensor positioned close enough to a power amplifierof the additional wireless transceiver to sense thermal energy generatedby the power amplifier and mitigation levels are positively correlatedwith temperatures as sensed by the thermal sensor.
 6. The method asclaimed in claim 4, wherein the state information includes whether theadditional wireless transceiver is currently transmitting.
 7. The methodas claimed in claim 4, wherein the state information includes anidentification of a type of network to which the additional wirelesstransceiver is currently connected.
 8. The method as claimed in claim 4,wherein the state information includes an indication of a transmit dutycycle of the additional wireless transceiver.
 9. The method as claimedin claim 4, wherein the state information includes an indication of atransmit power of the additional wireless transceiver.
 10. The method asclaimed in claim 4, wherein the additional wireless transceiver is acellular modem.
 11. The method as claimed in claim 4, wherein theadditional wireless transceiver is a wireless personal area networktransceiver.
 12. An apparatus comprising: a host processor; a wirelesslocal area network (WLAN) transceiver; one or more sensors; a memorycoupled to the host processor, the memory storing a mitigation managerand a WLAN driver, wherein the mitigation manager, when executed by thehost processor, is to determine, from time to time, from among multiplemitigation levels a mitigation level applicable to the apparatus as afunction of output from the one or more sensors, each of the multiplemitigation levels corresponding to a set of configuration changes for aMedia Access Control (MAC) layer of the WLAN transceiver, and whereinthe WLAN driver, when executed by the host processor, is to receive theapplicable mitigation level from the mitigation manager and to configurethe MAC layer of the WLAN transceiver according to the set ofconfiguration changes that corresponds to the applicable mitigationlevel, wherein configuring, when an applicable mitigation level hasincreased from a most recent previously determined mitigation level, theMAC layer of the WLAN transceiver to increases one or more interframespacing parameters of the MAC layer and the WLAN to decreases the one ormore interframe spacing parameters.
 13. The apparatus as claimed inclaim 12, wherein the one or more sensors comprise a proximity sensorand mitigation levels are negatively correlated with a distance of theapparatus to a human head or to a human lap as sensed by the proximitysensor.
 14. The apparatus as claimed in claim 12, wherein the one ormore sensors comprise a thermal sensor positioned close enough to apower amplifier of the WLAN transceiver to sense thermal energygenerated by the power amplifier and mitigation levels are positivelycorrelated with temperatures as sensed by the thermal sensor.
 15. Theapparatus as claimed in claim 12, further comprising an additionalwireless transceiver, wherein the applicable mitigation level isdetermined as a function of state information for the additionalwireless transceiver.
 16. The apparatus as claimed in claim 15, whereinthe one or more sensors comprise a thermal sensor positioned closeenough to a power amplifier of the additional wireless transceiver tosense thermal energy generated by the power amplifier and mitigationlevels are positively correlated with temperatures as sensed by thethermal sensor.
 17. An apparatus comprising: a host processor; anintegrated circuit coupled to the host processor, the integrated circuitcomprising: a dedicated processor; a wireless local area network (WLAN)transceiver coupled to the dedicated processor, the WLAN transceiverhaving a configurable Media Access Control (MAC) layer; a thermal sensorcoupled to the dedicated processor, the thermal sensor positioned closeenough to a power amplifier of the WLAN transceiver to sense thermalenergy generated by the power amplifier; and a memory coupled to thededicated processor, the memory storing a mitigation manager, which,when executed by the dedicated processor, determines, from time to time,from among multiple mitigation levels a mitigation level applicable tothe apparatus as a function of output from the thermal sensor, each ofthe multiple mitigation levels corresponding to a set of configurationchanges for a Media Access Control (MAC) layer of the WLAN transceiver;and a host memory coupled to the host processor, the host memory storinga WLAN driver which, when executed by the host processor, is to receivethe applicable mitigation level from the host processor and to configurethe MAC layer of the WLAN transceiver according to the set ofconfiguration changes that corresponds to the applicable mitigationlevel, wherein configuring, when an applicable mitigation level hasincreased from a most recent previously determined mitigation level, theMAC layer of the WLAN transceiver to increases one or more interframespacing parameters of the MAC layer and the WLAN to decreases the one ormore interframe spacing parameters.
 18. The apparatus as claimed inclaim 17, further comprising a proximity sensor coupled to the hostprocessor, wherein the mitigation manager, when executed by thededicated processor, determines the applicable mitigation level as afunction of output from the proximity sensor, and mitigation levels arenegatively correlated with a distance of the apparatus to a human heador to a human lap as sensed by the proximity sensor.
 19. The apparatusas claimed in claim 17, wherein mitigation levels are positivelycorrelated with temperatures as sensed by the thermal sensor.
 20. Theapparatus as claimed in claim 17, wherein the integrated circuit furthercomprises an additional wireless transceiver and the applicablemitigation level is determined as a function of state information forthe additional wireless transceiver.
 21. The apparatus as claimed inclaim 20, wherein the thermal sensor is positioned close enough to apower amplifier of the additional wireless transceiver to sense thermalenergy generated by the power amplifier of the additional wirelesstransceiver.